Sunday, March 7, 2010

First Microbes Colonized Land by Using Fat For Protection

The earliest microbes that survived on land may have synthesized fat molecules to prevent their death from dehydration.

The molecules, called wax esters, could have helped the microbes colonize land by protecting them against the harsh environments that probably characterized the lifeless continents, scientists hypothesizes in the March issue of Geology .

“Production of [wax esters] may represent an adaptation to cross a critical evolutionary threshold, i.e. surviving dehydration and/or dessication cycles,” wrote David Finkelstein, a biogeochemist at the University of Tennessee-Knoxville, and his co-authors. “This adaptation could have facilitated bacterial migration into the earliest lakes, and aided survival in terrestrial environments.”

Little is known about early terrestrial microbial life, which probably colonized land sometime before 500 million years ago. Unlike animals, they don’t leave behind much that scientists can find. But these organisms prepared the way for more complex life by seeding the land with organic compounds that became soil.

Finkelstein’s team has been investigating the behavior of modern communities of microbes called “microbial mats” in seasonal lakes near Warner Valley, Oregon. They found that dessicated mats have nearly double the amount of wax esters as their hydrated brethren, implying that the microbes start producing the molecules when times get tough.

When a microbe makes a wax ester from the molecules available to it, it also generates a water molecule. So, making esters could be a way of helping cells survive in environments with varying levels of moisture.

“It’s a really cool idea if it actually turns out in a concrete way that this is a way of waterproofing yourself and forestalling the loss of cellular water,” Finkelstein told Wired.com. “The first microbial mass that colonized land sure would have needed some kind of adaptation like this to make it successful.”

Beyond the ability to survive drying out, microbes would have also needed a way to spread across the land. Finkelstein believes that the dessicated mats could have been transported long distances by wind. The idea came to his team when they were at one of the lakes in Oregon.

“You could see mats blown out of the water and up the hills,” Finkelstein said. “Once the mat makes it to the top of the hill, you could blow into the next lake basin. If you could survive the drying, you could rehydrate yourself and live on.”

The next step in their research will be to look for telltale microbial wax esters deeper in the geological record. In doing so, they’ll be looking back through time, and it’s possible they’ll find them or other molecules that suggest they once existed. If they do, it will go a long way towards indicating that these fatty molecules were key to the evolution of terrestrial life as we know it.